Fix handling CRC64 of data blocks with length 0.

src/open.c

@@ -387,6 +387,8 @@ void* aaruf_open(const char* filepath)
                     break;
                 }
 
+                if(blockHeader.length > 0)
+                {
                     crc64 = aaruf_crc64_data(data, blockHeader.length);
 
                     // Due to how C# wrote it, it is effectively reversed
@@ -401,6 +403,7 @@ void* aaruf_open(const char* filepath)
                                 blockHeader.crc64);
                         break;
                     }
+                }
 
                 // Check if it's not a media tag, but a sector tag, and fill the appropriate table then
                 switch(idxEntries[i].dataType)